Radio receivers are conventionally tuned by pushbuttons which move the treadle bar. The treadle bar typically drives a carriage to move slugs within coils to vary the inductance in the tuning circuit to thereby tune the receiver to the predetermined frequency.
Advances in electronics technology have made possible fully electronic tuning of a receiver by simply controlling the voltage of a varactor, for example, in the tuning circuit of the receiver. It is known to use a potentiometer to provide the variable output voltage needed to control the varactor for tuning the receiver. However, it has been a continuing problem to find an efficient, durable and inexpensive arrangement for mounting the potentiometer in the tuner so that actuation of the pushbuttons for automatic tuning positions the movable elements of the potentiometer to provide the output voltage corresponding to the selected frequency. In an AM-FM receiver, for example, it has been proposed to provide a plurality of rotary potentiometers for the AM portion of a receiver and a second plurality of potentiometers for the FM portion of the receiver with appropriate gearing arrangements to couple the pushbuttons to the potentiometers and/or to the manual tuning shaft. It is also known to provide slide actuated potentiometers for each pushbutton for direct positioning of the potentiometer by the pushbutton. These solutions are expensive and very complex.
What has been needed is a mechanism which uses a single potentiometer mounted in the tuner which is responsive to actuation of any of the pushbuttons or the manual tuning shaft. The solutions that have been offered prior to this invention using a single potentiometer provide too much backlash (lost motion).
Further disadvantages of all of the aforesaid proposed solutions include too much driving force applied to the pushbuttons or manual tuning shaft and excessive additional parts which make the manufacturing costs prohibitive. For example, typical solutions which have been proposed required independent bearings supporting the potentiometer in addition to the bearings already provided in the tuner which support the treadle bar.